The application of UV/O3 process on ciprofloxacin wastewater containing high salinity: Performance and its degradation mechanism

Abstract

The increasing discharge of high-salinity organic wastewater has drawn much concern. This work investigated the degradation and mineralization of ciprofloxacin (CIP) in high-salinity wastewater by ozonation coupled with ultraviolet irradiation (UV). After coupling with UV, the removal efficiency of CIP was increased insignificantly (maximum 5.0%), while the dissolved organic carbon (DOC) removal in CIP wastewater (CW) was enhanced dramatically to 91.4% as compared with independent O3 (37.5%). The reactive oxygen species (ROS) were identified as singlet oxygen (1O2) and superoxide anion radical (O2−•)·through electron paramagnetic resonance (EPR) and quenching experiments, among which 1O2 predominated in the UV/O3 process. The existence of salt (Na2SO4 or NaCl) accelerated the mass transfer of O3 at the gas-liquid interface, thus CIP removal was promoted in UV/O3/SO42− system. However, excessive Cl− inhibited the removal efficiency of DOC in CW owing to its consumption of O3. CIP degradation decreased as pH increased in non-salinity and UV/O3/SO42− system, which proved the direct reaction occurred between CIP and O3. On the contrary, the O3 mass transfer increased with increasing pH, hence the elimination of DOC in CW was promoted in UV/O3/Cl− system. Volatile organic compounds (VOCs) were detected from tail gas, but the toxicity estimation indicated the toxicity of products was similar or less than that of CIP. Overall, this work is meaningful for the practical application of UV/O3 process in the high-salinity industry.